Method of making tin plate



Sept. 4, 1945. Q GLOCK 2,384,086

' METHOD OF MAKING TIN FLA-TE Filed Dec. 22, 1939 karieszf 6206i uctmore abrasion Patented Sept. 4, 1945 Charles-E. Glock, Baltim Crown Cork& Seal ore, Md., assignor to mpany,

Inc., Baltimore,

Md., a corporation of New York Application December 22, 1930, Serial No.310,650

3 Claims.

This invention is an improved tin plate and I method for preparing'same.

One object of the invention is to provide tin plate with a tin coatinghaving enhanced rust resistance.

Another object of the invention is to provide tin plate with a surfaceof increased hardness. The hardness characteristic renders theprodresistant and materially lessens the likelihood of scratching andincipient oxidation of the base.

A further object of the invention is to produce tin plate having ahigher lustre and smoothness as compared with tin plate heretoforeavailable. Since tin plate is employed frequently because it is desiredto give a nice appearance to an article, the presence of a surfacehaving an lmproved polish is very desirable.

An additional object of the invention is to produce tin plate having anincreased affinity for lithograph and printing inks as well asdecorative and protective lacquers and paints. Such coatings, as wellknown, are frequently applied to tin boxes, cans, container closures andother marked distinction to hot-dip tin plate which lraeggise of thepresence of oily residue frequently e s a coa mg or allows the rubbed onsame to be readily Another object of the invention is to provide tinplate having enhanced temper and workability. That is to say, the tinplate of this invention can be fabricated, as by stamping, drawing orother metal working operations into various shapes without danger of themetal cracklng or of the tin coating peeling or flaking from the metalbase.

,3 Of equal importance with the foregoing, it is an obJect of theinvention to provide a method which is simple and economical inoperation. This method embodies a combination of steps comprising (1)electrolytically coating the base metal with tin followed by (2) a skinpass treatment in the nature of a high presure cold-rolling.

- Not only is an improved product obtained by this substantially uniformin thickness, and has increased adherence to the base metal, asevidenced by the ability of the tin plate to. resist peeling and flakingwhen subjected to severe metal working operations.

An additional object of the invention is to provide a method whereincontinuous base metal strip or sheets of increased width, as compared tosheets platable by methods heretofore available, may be tin plated withfacility. I have found that base metal having a width of 30 inches ormore may be readily plated by the method of the present .invention.purposes, ability to increase the width of the tin plate affords asubstantial economy, as in the manufacture of container closures andcontainers.

I havefound that in order to obtain a coating having the requiredbrightness and other characteristics, it is necessary to controlcritically the pressure or the resulting elongation or reduction of themetal in the first pass through the mill in the cold-rolling operation.In other words,'I have found that successive passes will not produce thedesired characteristics if a minimum elongation or reduction is notobtained in the first pass. For example, in reducing by cold-rolling, Ihave found that the first pass should produce an elongation of the orderof at least inches for each 25 linear inches. Although I have found noobjectionable maximum elongation, it is observed that very satisfactoryresults have been obtained when elongation varies from to 5% inches foreach 25 linear inches.

Stated in terms of reduction in gauge, I find that the reduction in thefirst pass should be at least of one percent, which may be increased asdesired. So far as the brightness of the coating is concerned, I havefound no objectionable maximum reduction below which the reduction mustbe maintained in the first pass. However, it is desirable that thereductionnot reach a point where the strip is objectionably deformed asindicated by bowing or wrinkling. Consequently, the percentage ofreduction in the first pass should be maintained below that which willcause such strip deformation. Subsequent passes do not destroy theeffects obtained in the appearance of the metal when the elongation orreduction in the first pass is controlled in this manner. Stated interms of pressure, I have found that the rolls of the mill should beadjusted to apply a pressure of'the order of from at least 250,000 to500,000 lbs. Such a range of For many finish and coincident reductionwhen rolling, for example, a strip 30 inches wide and having a gauge ofapproximately .011 inch. This pressure may be determined intheconventional way, by an instrument employed to register the elongationof the mill housing during the application of pressure. Suchinstrumentsare well known and are employed on substantially all types of rollingmills. The particular figures given were taken from such instrumentapplied to a 4-high Mesta tempering mill. When so controlled, theelongation and gauge reduction is of the order above recited. The metalmay be fed through the mill at a rate of from 1200 to 2000 feet perminute.

.11; is, of course, well known that tin plate is relatively expensivebecause of the cost of the tin. With this invention, it has been foundthat smooth, nice-appearing coatings affording the desired protection ofthe base metal for certain uses such as for dry packages can be producedwith as little as 1 5 pound of tin per base box. By base box, I meanthe. area represented by -112 sheets of size 14 by 20 inches, i. e.,substantially 33,000 square inches. Of course, coatings of increasedweight may be applied with equal emciency; and the method lends itselfto-regulation of 'the weight as desired. As is well known, by thehot-dip method, it is not ordinarily possible to reduce the weight ofthe coating below 1 /3 pounds per base box.

Economy in manufacture is important since tin plate is employeduniversally and particularly in the manufacture of numerous articleswhich must be sold at a very modest price.

For a more complete understanding of the invention reference is had tothe accompanying drawing wherein Y Figure 1 is a diagrammaticillustration of the electro-coating operation;

Figure 2 is 'a diagrammatic illustration of the cold-rolling step; and

Figure 3 is a diagrammatic view showing the manner in which'theelectro-coated band is continued to the cold-rolling instrumentality.

In practicing the invention, the customary steel or black iron ofappropriate gauge is utilized. The metal is usually annealed and issupplied in continuous strips in the form of rolls by the steel mill,

, 1, is mounted upon a conventional uncoiler for feeding the stripcontinuously to the electrolytic coating apparatus. The numeral llindicates an apparatus for welding ends of the strips together and thenumeral l2 indicates a table having a holding clamp to maintain one endof the strip during the welding operation. The numeral l3 indicates theacid pickling tank which generally contains hydrofluoric or othersuitable acid while the numeral N indicates a cold water rinsing tank.The strip I just prior to entering the electrolytic both I5 is heated bymeans of steam jets I6 to a temperature of about 160 F. The wiping rollsI! are of the character to permit a film of water to remain on the stripsubstantially until it enters the bath, whereby the strip is protectedagainst the efiects of oxidation by the air and is introduced to thebath at a temperature to promote optimum coating and withoutsubstantially reducing the temperature of the bath. As will beunderstood, the heating means employed, namely, steam application is ofa character which will not dry the surface of the strip; ,there issuflicient condensation of the steam to maintain 2,884,086 7 the desiredprotective moist film. The strip is fed through the'bath at varyingspeeds which may be as high as 500 feet a minute or greater. It will benoted that in the bath the strip is coated while traveling in verticallydisposed position. The chemical reagents employed are preferably sodiumstannate 5.4 ounces to 13 ounces; sodium acetate 2 ounces to 5 ounces;and caustic soda 1 ounce to 3 ounces, per-gallon of water. In somecases, sodium cyanide is included in the bath in an amount to insurethat the electrodes corrode uniformly, for example, about 1 ounce to 6ounces, per gallon of water.

The current density is maintained between 10 and '75 amperes per squarefoot of cathode (strip) and the temperature of the bath is. generallysubstantially between 158 to 200 F. As will be understood, the weight ofthe coating may be controlled by varying the time to which the strip issubjected to the bath as by regulating the speed of travel of the stripor by varying the amperage or by doing both.

From the bath, the coated strip is led through a cold water rinsing tankl8 and then through a hot water rinsing tank 19 whereupon it travelsthrough a tensioning mechanism 20 and is wound into coils 2i. The coatedmetal is dull and soft and will have a thickness or weight of tin coatcontrolled in accordance with the use to be made of the tin plate.

The coils of coated metal are each transferred to a suitable uncoilerfor continuously'feeding the strip to the cold-rolling instrumentalitywhich is in the form of a usual a-ihigh mill as shown'at 22 in Figure 2.In this mill, the coated sheet is given a skin, pass treatment by meansof a high pressure cold-rolling to impart thev properties of rustresistance, smoothness, hardness, temper and workability, and highlustre in a manner appreciably better than present available tin platenow possesses. The apparatus disclosed has the rolls rotating at uniformspeed.

I have discovered that cold-rolling of tin coated metal, andparticularly metal which has been electrolytically coated with tin, verysubstantially contributes to producing the aforesaid improved propertiesof. the'tin plate. That is to say, as above explained, I have found thatin order to obtain a .coating having the required brightness 'and otherimproved characteristics, it is necessary to control critically (1) thepressure or (2) the resulting elongation or (3) the reduction of themetal in the first pass through the mill in the cold-rolling operation.It willbe observed that the skin pass treatment is decidedly rapid, andsince the metal is fed as a continuous strip and only a single skin passtreatment is required a substantial economy is efiected in addition tostantially higher than tin plate of the same weight which has not beencold-rolled.

Moreover, the improved polish or high lustre of the tin plate isappreciable and 'very materially enhances the appearance of the product.

Since the principal purpose of coating steel with tin is to (1) protectthe metal; and (2) beautify the same, it will be understood that both ofthese characteristics are substantially improved by the presentinvention.

By way of example, a continuous strip of steel having a thickness ofsubstantially .011" which i is customarily used for making "crown" tinplate is provided in accordance with this invention with a tin coatinghaving a weight of approximately one half to three quarters of a poundper base box. The ingredients employed per gallon of water are sodiumstannate-8 ounces; sodium acetate-3 ounces; caustic soda 1.6 ounces.-Sodium cyanide was included in the bath in an amount to assure that theelectrodes corrode uniformly, for example, 3 ounces per gallon of water.The current density was maintained at 16 amperes per square foot ofcathode (strip) and the bath temperature was of the order of 175 F. Themetal was introduced to the bath at a temperature of about 125 to 160 F.

The coated metal as produced was formed into a roll 2i. The rolls of themill 2! through which the strip is now continuously fed are adjusted toexert a pressure of the order of 500,000 lbs, and at the bight of therolls the pressure exerted per linear inch transversely of the stripupon the coated metal is about 17,000 lbs. The speed of travel of thestrip is 1200 feet per minute. In

having a uniform coating which completely covera the metal base. Ofparticular importance, the coating is smooth and continuous and has themeasure of rust resistance and in the present case rust resistance issubstantially higher than with a comparable weight of hot-dip tin plate.The product is diflicult to scratch indicating a desirable hardness andis readily worked without cracking and without peeling or I flaking ofthe tin coat. Likewise, the product I permanently retains decorative andprotective this manner, the critical conditionsof cold-rollsoahighlustre. Continuityofthetincoatdmotes m coatings much better thanconventional tin plate.

From the foregoing, it will be appreciated that the combination ofelectrolytic coating and high pressure cold-rolling produces a verysatisfactory product and affords a rapid and economical method.

In some cases, instead of collecting the coated plate in a roll 2|, thestrip may be continued so as to be passed directly to the cold-rollingmill 22 as showninFigure 3.

'In connection with the electro-plating operation, it is sometimesdesirable to give the band a cold-rolling treatment before it enters thebath, i. e., before the acid pickling, in order to properly temper thestrip.

The invention may be applied in connection with any suitable gauge ofbase metal and any appropriate weight of tin coating and while the metalis preferably fed as a continuous strip, the product may be formed insheets of any desired length.

I claim:

l. The method of making tin plate which comprises electrolyticallycoating tin on iron strip and cold rolling the coated metal with rollsrotating at uniform speed and under a pressure of from 250,000 pounds to500,000 pounds to elongate the metal at least inch for any linear 25inches in a single pass through the rolling instrmnentality and toimpart a smooth, lustrous surface to the electroplated strip.

2. The method according to claim 1 wherein the coated metal is traveledbetween the rolls at a speedo! substantially 1,200 to 2,000 feet perminute. a

3. The method according to claim 1 which comprises exerting a rollpressure of 500,000 pounds and-a pressure at the bight of the rolls ofabout 17,000 pounds per linear inch transv'ersely of the strip.

CHARLES E. GLOCK.

